Within the last thirty years, U.S. aquaculture production has grown from a farmgate value of around $100 million to nearly 500 million dollars. Pond production continues to dominate aquaculture production. Pond reared catfish account for nearly half of the total U.S. aquaculture production, with the majority of this production emerging from four states: Mississippi, Alabama, Arkansas, and Louisiana.
Within these same three decades pond culture practices have undergone major changes. The industry demand for water has been the driving and shaping force for pond aquaculture. Mississippi dominates pond fish culture because of the availability of large volumes of shallow groundwater in the Mississippi delta region. However, even in Mississippi, the availability of water and land suitable for pond aquaculture continues to diminish. As a result, the farmers have been under on-going pressure to intensify production. In the early days production was limited to the biomass that wind driven re-aeration could support. In the late 50's, Alabama's Auburn University was recommending catfish farms target harvests at around 1300 lbs/acre. In 1969, catfish production averaged 1100 lbs/acre with a total production of 44 million lbs with good managers achieving 1500 lb/acre. The 1997 production was projected at 520 million lbs on 164,000 acres of ponds for an average farm production of 3200 lbs/acre. Well managed farms are estimated to be producing 4000-5000 lb/acre. To achieve these increased carrying capacities, producers added first emergency aeration, then routine nightly aeration and in some cases of very high carrying capacities 24-hr aeration. One to two hp per acre aeration is now standard practice in the industry. Occasionally, farmers will report 7000-8000 lb/acre of production, with researchers sometimes achieving as high as 12,000 lb/acre. However, pond production in excess of 5000 lb/acre which corresponds to peak feed applications of 80-100 lb/acre, is not routinely successful. In particular, it has been difficult to maintain oxygen at sufficient levels to meet the above production rates. Further, even if oxygen needs are met at these levels, total ammonia concentrations from livestock waste often reach limiting or toxic levels.
In pond cultures, oxygen levels are maintained by the presence of Algae. Another problem experienced at high production rates are Algal "bloom and crashes". This situation tends to lead to a succession of algal species, in particular blue green algae, which can result in a undesirable "off flavor" produced by an unwanted algal population dominating the pond, causing the flesh of the fish to have an unacceptable taste and odor.
At present, the problem remains as to whether pond fish production can be increased to meet future demands. In a raceway, the fish carrying capacity is ultimately limited by the accumulation of toxic metabolites such as NH3 and CO2, distributed into the water flow. If the water is to be used for additional fish culture, then specific waste treatment processes must be added to the flow path to remove the limiting metabolites. In contrast, in pond culture, the pond is both the waste treatment process and culture containment. The basic treatment process of the pond is algal photosynthesis, while some effort has been made to eliminate algal growth to encourage other treatment processes such as nitrification or NH3 volatilization, most successful pond culture practices continue to be tied to management of highly eutrophic "green water" systems. However, the algal growth observed in typical ponds receiving the typical maximum feed application rate of 80-100 lb/acre-day rarely exceeds sustained levels 1-3 gm C/m2-day. In contrast, high rate algal production ponds are routinely operated at sustained levels of 6-12 gm C/m2-day. Algal production systems are designed to maintain uniform water velocities throughout the culture volume. This ensures that no horizontal or vertical stratification occurs. Therefore 100% of the water column is utilized. In addition the algal cell population is maintained at a young cell age (1-2 days) either through direct harvesting of the algal biomass or by control of system hydraulic detention time.
These observations suggest that the pond treatment capacity and therefore fish carrying capacity can likely be increased by reconfiguring the pond to maintain a uniform velocity and mixing profile throughout the entire pond. An additional advantage of creating a velocity profile in the pond allows for the different processes occurring in the pond, fish culture, solid waste removal, algal harvest, gas exchange to be compartmentalize in a series processes subject to more control by the operator, and consequently more reliable and predictable.
To date, the development of pond aquaculture has paralleled developments in other fields of agriculture, a trend resulting in the need for increased productivity, less labor, more automation, more process control, with higher degree of reliability and consistency of production. The social and market forces driving these changes are likely to intensify. We can expect future pond aquaculture to move from "farming" the waters to true production systems in which manipulated "ecosystems" (the fish pond) are redesigned into a series of more controllable fish production and waste treatment processes. The major counter balancing force will be the need to constrain costs.
A pilot scale aquaculture system is disclosed in an article entitled: "Design of a Partitioned Aquaculture System" by Drapcho, et al. which was written for presentation at the 1989 International Winter Meeting of the American Society of Agricultural Engineers.